One of the most common light fixtures is the recessed can downlight (RCD), which is an open-bottom can that contains a light bulb, most commonly an incandescent bulb. The fixture is typically connected into the power mains at 120 to 277 volts, 50/60 Hz. RCDs are generally installed during the construction of a building before the ceiling material (such as plaster or gypsum board) is applied. Therefore, they are not easily removed or substantially reconfigured during their lifetime.
RCDs generally also accommodate incandescent light bulbs of various sizes (which, in a 4-inch-diameter RCD, include A19 (the common Edison-base bulb), PAR20, PAR16, R16, R20, etc., where the numerical designation refers to the diameter of the bulb and the letter to the bulb type or shape). These bulbs all have different overall dimensions (i.e., length, width, and diameter), and have varied light-distribution capabilities. For example, various bulbs have narrow, medium, or wide (flood) distributions. Therefore, the internal features of the RCD are constructed to accommodate many (if not all) various bulb types. Such features include mechanisms to adjust the vertical position of the bulb socket, as well as various “face plates” that cover the bottom of the fixture and provide a decorative finish that fits flush with the ceiling. Moreover, the face plate may contain a recessed reflector which channels and distributes the light. Because there are so many different light bulbs and finishes, there are a very large number of trim rings and optics combinations, in addition to the various spacers that accommodate the bulbs. Thus a complex arrangement of parts is needed for each RCD that is produced.
Because LEDs have very high efficiency (e.g., 100 lumens per watt compared to 10-15 lumens per watt for incandescent or halogen lights) and a long lifetime (e.g., 10,000-100,000 hours), they are attractive for virtually all lighting applications. However, even a dedicated LED-based downlight would have the disadvantage of only being compatible with new construction (without a prohibitively costly overhaul of an entire lighting system and related infrastructure), and thus would be unavailable for retrofitting into the large host of existing incandescent-based RCDs. Moreover, because the LED technology itself is rapidly changing, LED-based fixtures become obsolete as the LED technology, as well as the optics and cooling technology vital to performance, improve.
LED-based light bulbs represent a logical alternative. These products contain electronics, optics and heat sinks all in a form factor identical to that of the particular light bulb to be replaced. Such designs may be quite difficult to achieve, however, and generally necessitate strict control over power consumption in order to maintain low enough operating temperatures to avoid thermally-induced premature failure. Hence, the light output of such LED light bulbs is typically well below that of the incandescent light bulbs they replace. For example, a PAR20 LED lamp from Lighting Sciences has a rated output of 350 lumens while a conventional 50 watt PAR20 incandescent bulb has light output in the range of 600-750 lumens. Furthermore, replacement of the light bulb product means disposing and replacing the entire suite of electronics, optics, and heat sink—a costly and wasteful proposition.
Thus, there is a need for retrofit devices for RCDs based on LEDs that are compatible with a wide range of differently sized and/or shaped RCD fixtures, and that are easily upgradable with different light sources and/or associated electronics.